The invention is directed to an improved wax composition which can be coated on paper products and which makes the paper products recyclable under standard repulping condition in a hydropulper without significantly increasing the repulping temperature or pH. The invention is also directed to a wax-coated paper product which is capable of being recycled under standard repulping conditions.
Wax-coated paper products, particularly wax-coated corrugated paperboard containers have been used for years to ship and store fresh, perishable foods such as poultry, fish and meat. Typically, the containers are packed with crushed ice to keep the food cool during shipping and storage. The wax imparts water and moisture resistance to the containers.
Examples of wax-coated or wax-impregnated paperboard containers are described in U.S. Pat. Nos. 3,892,613 to McDonald et al.; 4,017,016 to Ivy; 4,126,225 to Hyland et al.; and 4,948,033 to Halsell, II et al. As shown in Halsell, II et al., the paperboard may be impregnated with about 6 pounds per 1,000 square feet of a wax blend and then curtain coated with an additional 6.5 pounds per 1,000 square feet of wax blend.
Currently, wax-coated containers are not recycled for several reasons. In view of the large quantity of wax-coated containers which are used each year, it would be highly desirable to recycle the containers rather than to simply discard them. The reclamation of waste paper has been the subject of various patents and studies. For example, U.S. Pat. Nos. 3,440,134 to Murphy, Jr., 4,347,009 to DeCuester et al.; 4,548,674 to Hageman wt al.; and 4,737,238 to deRuvo, are related to methods for pulping waste paper and, particularly, used corrugated containers.
Several problems are inherent in recycling wax-coated containers. First, the purpose of the wax is to impart water and moisture resistance to the container and this property directly interferes with the essential property required in a recyclable container, namely, repulpability. Hence, it is necessary to remove the wax coating in the recycling process. Second, in removing the wax coating, a wax residue may remain on or contaminate the paper fibers. This residue weakens the strength of the recycled sheet because it prevents or reduces the amount of interfiber bonding such as hydrogen bonding which can be achieved in the sheet. Third, due to the high melting points of many of the waxes conventionally used on wax-coated containers, in order to remove the coating, it is necessary to modify the industry standard repulping conditions to use higher repulping temperatures. This can lead to increased energy costs which detracts from the profitability of recycling.
Presently used corrugated container boards are received at the pulping station in large bales. As a result of the difficulties involved in repulping wax-coated containers, if an inspection of the bales reveals the presence of an excessive amount of wax-containing board, the entire bale is discarded rather than repulped. While this may not represent a serious economic loss, it is certainly an important environmental concern.
In order to recycle wax-coated containers, it would be desirable to design a wax coating which can be cleanly removed from the containerboard under conventional or industry standard repulping conditions of temperature and pH. Aluminum soaps have been proposed as a substitute for wax in recyclable wax-coated containers for this purpose, and the use of aluminum soaps in combination with fatty acids has also been considered. However, a hot dispersion technique and an alkaline pH are required to remove these coatings and there remains a need for a coating which is compatible with industry practice.